This invention relates to a water-based fluorine-containing emulsion used for a water-based paint.
Hitherto, fluoropolymers prepared from a monomers' composition containing a fluoroolefin have widely been used for paints, because these polymers are superior in weather resistance. For example, there is known a copolymer prepared by copolymerizing a fluoroolefin, an aliphatic vinyl ester such as vinyl acetate, and another monomer (see JP-B-4-40865). This copolymer is soluble in various solvents, and is used for preparing paints that are curable at ambient temperature and are used in the fields of architecture and the like. These paints, however, each contain a relatively large amount of organic solvent. Therefore, there are risks of fire, a hazard to human body, air pollution, and the like. In view of this, there has been a demand for non-organic-solvent paints, particularly for water-based paints. To meet this demand, there have been a lot of researches into water-based fluorine-containing paints that are curable at ambient temperature. An emulsion used for these paints is generally produced by emulsion polymerization, using a large amount of emulsifying agent. This emulsifying agent remains even in a film prepared by applying a water-based paint to a substrate, thereby increasing coefficient of water absorption of this film. Thus, this film is inferior to those prepared by applying organic solvent type paints, in water resistance and stain resistance. In view of this inferiority, there have been other researches into water-based fluorine-containing paints each prepared by using a monomer containing an alkoxysilyl group which is a cross-linking group (see JP-A-4-202484 and JP-A-5-25421). It is, however, difficult to obtain both of a satisfactory stability of this alkoxysilyl group (cross-linking site) in emulsion and a satisfactory degree of cross-linking of a paint's polymer after formation of the coated film, because these characteristics conflict with each other. In other words, if such water-based paint is made satisfactory in the cross-linking degree, this paint becomes unsatisfactory in emulsion stability during storage. In contrast, if such water-based paint is made satisfactory in emulsion stability during storage, this paint becomes unsatisfactory in the cross-linking rate, thereby making the coated film inferior in water resistance in its early stages. In view of this, it has been proposed to add a catalyst for increasing the cross-linking rate of this paint, immediately before the application of this paint. With this, however, this paint becomes a two-package paint that is inferior to a one-package paint in workability.